Actually on the height thing, that kinda happens to me. I am only 5'4, but people often think of me as taller. My own sister in law had known me for 5 or so years before she became aware that at 5'8 she was taller than me. For whatever reason, she always saw me as taller than her.

I would think she were sightly obtuse except it was not the first or last time similar things have happened to me. Even my own husband is surprised every now and then at just how short I really am. Sometimes he completely misjudges it and kisses me on the forehead.

A number of possibilities:1. She is a fairy, and is 300 years old but looks like she's 21.2. She, as Claire, Kaitebon and Anonymous said, is bound to the pirates until her 84th birthday and was born on leap-day, so she's 84 now, yet if we go by birthdays she is only 21.3. Gilbert wrote the character breakdown, but mistakenly wrote that she is older rather than younger.4. She is a ghost who died at 21.5. She counts her age in dog years.